HOMER CITY, Pennsylvania — There’s no sign for Nonlethal Technologies when you drive past the pair of faded yellow gates on the side of the highway in western Pennsylvania.

Despite its name, there isn’t much sign of any technology once you get inside the gates, either — there are just a few rows of worn-looking shipping containers clustered together. But the little-known company is a major exporter of tear gas and other crowd-control equipment and has sold supplies to a number of countries, including repressive regimes, for years.

Most recently, hundreds of the company’s tear gas canisters have ended up on the streets of Hong Kong, where police have used them to crack down on pro-democracy protests that have rocked the city for more than three months. The demonstrations have shifted from large-scale marches that have brought as many as 2 million people to the streets to standoffs between police and protesters that often look more like guerilla warfare.

The trail of tear gas sailing through the air has become a familiar sight in Hong Kong as police launch round after round of these projectiles into the crowds of protesters. The acrid smell of tear gas is unmistakable — it fills your throat and nose and burns your eyes and skin, unless you wear a respirator. It can make you cough until you vomit.